Sorry but it's very contradicting what you say.. If the piston in the carb go's UP.. (when giving it throttle), then there MUST BE some vacuรผm pulled through it? Right?
You got 2 airflowmeters and have you switched them.. maybe one is broken?
Does the engine/car pull very well? i assume that the engine is also very weak? Something is blocking the throat of one carb, the engine works on just 1 carb and the other half works via the balance tube? take the inlet apart and see what's going on there!
I can't imagine that that engine runs very well and got over 120hp..
A video of it would be awesome.. a engine that runs on 1 rear carb and no air going through the front carb but the piston go's up anyway.. it's just impossible.. i guess...
I would take the inlet apart, maybe take a look inside the cylinders with a camera.. take a look at the valves.. etc.etc.